Sensitive data, such as encryption keys, saved on storage devices should be securely deleted when the device is moved from one computer to another or is taken out of service. However, this is not always possible. Modern rotating media transparently moves some parts of the storage to new locations if the media starts to develop errors. Flash storage or “solid-state disks” do this as a matter of course to even out the number of times that a given sector of the device has been used. The end result is that the high-level user of these mass storage devices cannot rely on overwriting data as a way of erasing it. Any time that a location on mass storage is written, there is a chance that the old data will remain on the device. While this is an unusual occurrence on rotating storage media, it is a common mode of operation on solid-state storage. Consequently, highly sensitive information such as encryption keys must be protected by mechanisms that presume that there is always a chance that overwriting does not ensure the sensitive data has been destroyed.